Bump css-loader from 1.0.1 to 2.1.1 in /slides (#58)

Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 1.0.1 to 2.1.1.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](webpack/css-loader@v1.0.1...v2.1.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot[bot]

slides/package-lock.json

@@ -10,7 +10,7 @@
     "@babel/core": "^7.1.6",
     "babel-loader": "^8.0.4",
     "babel-preset-env": "^1.7.0",
-    "css-loader": "^1.0.1",
+    "css-loader": "^2.1.1",
     "file-loader": "^2.0.0",
     "html-webpack-plugin": "^3.2.0",
     "mini-css-extract-plugin": "^0.4.5",